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VNODE Write Processes

+ +## META Operations +META data write operations including: + +1. create table +2. drop table +3. alter table + +We take create table as an example to figure out the whole process. +```plantuml +@startuml create_table +skinparam sequenceMessageAlign center +skinparam responseMessageBelowArrow true + +participant APP as app +box "dnode1" + participant RPC as rpc + participant VNODE as vnode + participant SYNC as sync +end box + +box "dnode2" + participant SYNC as sync2 + participant VNODE as vnode2 +end box + +box "dnode3" + participant SYNC as sync3 + participant VNODE as vnode3 +end box + +' APP send request to dnode and RPC in dnode recv the request +app ->rpc: create table req + +' RPC call vnodeProcessReq() function to process the request +rpc -> vnode: vnodeProcessReq +note right +callback function +run in RPC module +threads. The function +only puts the request +to a vnode queue. +end note + +' VNODE call vnodeProcessReqs() function to integrate requests and process as a whole +vnode -> vnode: vnodeProcessReqs() +note right +integrate reqs and +process as a whole +end note + + +' sync the request to other nodes +vnode -> sync: syncProcessReqs() + +' make request persistent +' sync -->vnode: walWrite()\n(callback function) + +' replicate requests to other DNODES +sync -> sync2: replication req +sync -> sync3: replication req +sync2 -> vnode2: walWrite()\n(callback function) +sync2 --> sync: replication rsp\n(confirm) +sync3 -> vnode3: walWrite()\n(callback function) + +sync3 --> sync: replication rsp\n(confirm) + +' send apply request +sync -> sync2: apply req +sync -> sync3: apply req + +' vnode apply +sync2 -> vnode2: vnodeApplyReqs() +sync3 -> vnode3: vnodeApplyReqs() + +' call apply request +sync --> vnode: vnodeApplyReqs()\n(callback function) + +' send response +vnode --> rpc: rpcSendRsp() + +' dnode send response to APP +rpc --> app: create table rsp +@enduml +``` + +## Time-series data Operations +There are only one operations for time-series data: data insert. We will figure out the whole process. + +```plantuml +@startuml create_table +skinparam sequenceMessageAlign center +skinparam responseMessageBelowArrow true + +participant APP as app +box "dnode1" + participant RPC as rpc + participant VNODE as vnode + participant SYNC as sync +end box + +box "dnode2" + participant SYNC as sync2 + participant VNODE as vnode2 +end box + +box "dnode3" + participant SYNC as sync3 + participant VNODE as vnode3 +end box + +' APP send request to dnode and RPC in dnode recv the request +app ->rpc: create table req + +' RPC call vnodeProcessReq() function to process the request +rpc -> vnode: vnodeProcessReq +note right +callback function +run in RPC module +threads. The function +only puts the request +to a vnode queue. +end note + +' VNODE call vnodeProcessReqs() function to integrate requests and process as a whole +vnode -> vnode: vnodeProcessReqs() +note right +integrate reqs and +process as a whole +end note + + +' sync the request to other nodes +vnode -> sync: syncProcessReqs() + +' ' make request persistent +' ' sync -->vnode: walWrite()\n(callback function) + +' ' replicate requests to other DNODES +sync -> sync2: replication req +sync -> sync3: replication req + +' vnode apply +sync2 -> vnode2: vnodeApplyReqs() +sync3 -> vnode3: vnodeApplyReqs() + +' call apply request +sync --> vnode: vnodeApplyReqs()\n(callback function) + +' send response +vnode --> rpc: rpcSendRsp() + +' dnode send response to APP +rpc --> app: create table rsp +@enduml +``` + +## vnodeProcessReqs() +```plantuml +@startuml vnodeProcessReqs() +participant VNODE as v +participant SYNC as s + +group vnodeProcessReqs() + ' Group requests and get a request batch to process as a whole + v -> v: vnodeGetReqsFromQueue() + note right + integrate all write + requests as a batch + to process as a whole + end note + + ' VNODE call syncProcessReqs() function to process the batch request + v -> s: syncProcessReqs() + + group syncProcessReqs() + ' Check if current node is leader + alt not leader + return NOT_LEADER + end + + s -> s: syncAppendReqsToLogStore() + group syncAppendReqsToLogStore() + s -> v: walWrite() + note right + There must be a + callback function + provided by VNODE + to persist the + requests in WAL + end note + + alt (no unapplied reqs) AND (only one node OR no meta requests) + s -> v: vnodeApplyReqs() + note right + just use the woker + thread to apply + the requests. This + is a callback function + provided by VNODE + end note + else other cases need to wait response + s -> s: + note right + save the requests in log store + and wait for comfirmation or + other cases + end note + + s ->]: send replication requests + s ->]: send replication requests + end + end + end +end +@enduml +``` + + + + +## vnodeApplyReqs() +The function *vnodeApplyReqs()* is the actual function running by a vnode to process the requests. +```plantuml +@startuml vnodeApplyReqs() +skinparam sequenceMessageAlign left +skinparam responseMessageBelowArrow true + +participant VNODE as vnode +participant TQ as tq +participant TSDB as tsdb +participant META as meta + +group vnodeApplyReqs() + autonumber + loop nReqs + ' Copy request message to vnode buffer pool + vnode -> vnode: vnodeCopyReq() + note right + copy request to + vnode buffer pool + end note + + vnode -> tq: tqPush() + note right + push the request + to TQ so consumers + can consume + end note + alt META_REQ + autonumber 3 + vnode -> meta: metaApplyReq() + else TS_REQ + autonumber 3 + vnode -> tsdb: tsdbApplyReq() + end + + end + + ' Check if need to commit + alt vnode buffer pool is full + group vnodeCommit() + autonumber 4.1 + vnode -> tq: tqCommit() + note right + tqCommit may renew wal + end note + vnode -> meta: metaCommit(); + note right + commit meta data + end note + vnode -> tsdb: tsdbCommit(); + note right + commit time-series data + end note + end + end +end +@enduml +``` +